A number of modern uses have been found for non-woven materials produced from melt spun polymers, particularly degraded polyolefin-containing compositions. Such uses, in general, demand special properties of the nonwoven and corresponding fiber such as special fluid handling, high vapor permeability, softness, integrity and durability, as well as efficient cost-effective processing techniques.
Unfortunately, however, the achievement of properties such as softness, and vapor-permeability, for example, present serious largely unanswered technical problems with respect to strength, durability and efficiency of production of the respective staple and nonwoven products.
One particularly troublesome and long standing problem in this general area stems from the fact that efficient, high speed spinning and processing of polyolefin fiber such as polypropylene requires careful control over the degree of chemical degradation and melt flow rate (MFR) of the spun melt, and a highly efficient quenching step capable of avoiding substantial over- or under-quench leading to melt fracture or ductile failure under high speed commercial manufacturing conditions. The resulting fiber can vary substantially in bonding properties.
It is an object of the present invention to improve control over polymer degradation, spin and quench steps so as to obtain fiber capable of producing nonwoven fabric having increased strength, toughness, and integrity.
It is a further object to improve the heat-bonding properties of fiber spun from polyolefin-containing melt such as polypropylene polymer or copolymer.